The pristine state of unpolluted waterways may be their downfall, according to research results published in the journal Geophysical Research Letters.

Scuba-diving scientists are unrolling long rubber mats across the bottom of Lake Tahoe coves in an attempt to quell a clam invasion that could cloud the world-reknown cobalt waters. The half-acre mats are designed to smother dime-sized nonnative Asian clams that can reach populations of 5,000 per square yard.

Many streams and rivers in the United States are getting warmer, with the greatest increases in urbanized areas, according to research to be published in an upcoming edition of the journal Frontiers of the Ecology and the Environment.

A recent NASA study showed Lake Tahoe's water is warming twice as quickly as regional air temperature, lending weight to predictions of warming lake temperatures made by UC Davis researchers in 2008.

Airborne nitrogen pollution from vehicle exhaust and farm fertilizer is turning algae in the alpine lakes of Rocky Mountain National Park into junk food for fish, a study says. A similar phenomenon is occurring in Sweden and Norway, according to the study of about 90 high-elevation lakes set to be published in the journal Science on Friday.

In the world of alternative fuels, there may be nothing greener than pond scum.

The idea is to circumvent the kind of problem researchers face when they test one stream on a sunny day, another the next day after a rain, a third the following day when the algae are photosynthesizing to beat the band.